Performance Of Air Curtain Research Articles

Study on the Smoke Control Performance of Air Curtains in Emergency Stairwells of Multi-Unit Residential Buildings

Recently, in high-rise buildings, pressurization systems have been installed in emergency stairwells to prevent the ingress of smoke. However, in older buildings, these stairwells often lack pressurization systems, while in buildings with fewer stories, such systems are not typically installed. This study conducts simulations and a hot smoke test to evaluate the performance of air curtains in blocking smoke and toxic gases in outdoor emergency stairwells where additional pressurization equipment cannot be installed. The simulation results showed that air curtains installed perpendicular to the floor were useful at preventing smoke ingress, and higher wind speeds increased their effectiveness. It is believed that air curtains can partially reduce smoke ingress in stairwells of older buildings or low-rise structures without pressurization systems, thereby ensuring fire safety.

Preventing unwanted airflow at building doors

Data-driven model more accurately predicts air-curtain performance.

Performance and flow dynamics of heavy air curtains using experiments and numerical simulations

Performance and flow dynamics of heavy air curtains using experiments and numerical simulations

Correction: Yan et al. Numerical Simulation on the Smoke Prevention Performance of Air Curtains in an Island-Type Subway Station. Fire 2023, 6, 177

In the original publication [...]

A mixed numerical-experimental study of the outdoor wind effects on the indoor air distribution under the multi-nozzle air curtains

The infiltration of cold air through the open doors is controlled using air curtains, resulting in lower thermal loss and higher energy efficiency in the buildings. Meanwhile, severe outdoor conditions affect the performance of the air curtains drastically. In this context, the performance of a multi-nozzle air curtain with two different geometries has been investigated under various outdoor conditions using validated CFD. The air curtain system creates a thermal barrier with a specific sequence of large nozzles, small nozzles, and holes that blow air downward at different speeds. A half scale (1:2) model located above a door in the middle of the wind tunnel at the University of Sherbrooke is used for the hot wire measurements of the critical characteristics for different wind velocities (0, 4, and 9 m/s). Also, the SST k−ω turbulence model has shown the highest accuracy during the turbulence model sensitivity analysis and is used for complementary studies. Despite all the similarities, the results indicate that Fifth Order Polynomial Nozzles are more resistant against the high-velocity front winds, comparing the Arc Shape Nozzles, due to 3.6% augmentation of the exit velocities at large nozzles and shorter convergence areas. Also, this fact is proven by the studies of the impact point of these air curtains.

Numerical Simulation on the Smoke Prevention Performance of Air Curtains in an Island-Type Subway Station

Subway fires are a major threat to the safe and smooth operation of subway stations. In this paper, an island-type subway station was taken as an example to conduct a series of numerical simulations using Fire Dynamics Simulator (FDS). The temperature, visibility, and CO concentration in the subway station were analysed under different thicknesses and jet velocities of the air curtains. The smoke-prevention performance of the air curtains in the subway station was investigated. As the thickness and jet velocity increase, the flame tilts significantly, which greatly hinders the spread of smoke toward the stairs. The smoke temperature and CO concentration on the left side of the air curtains gradually decrease, while the visibility increases significantly. For a 3 MW fire scenario, to satisfy the evaluation criteria, the results show that the thickness of the air curtains needs to be at least 0.3 m, and the jet velocity needs to be at least 2 m/s. The sealing effectiveness (Esealing) tends to increase and then remains constant with increasing momentum, and the maximum is obtained when the momentum of the air curtains (Ia) is 12.5 kg·m/s2. Meanwhile, it is found that an energy-saving efficiency of 85.2% can be achieved by replacing positive pressure ventilation with air curtains. The results of this work can provide a significant reference for the design of smoke protection in subway stations.

Air curtains: validation of results from small-scale laboratory waterbath experiments by real-scale measurements in climate chambers and numerical simulations

An air curtain is a planar turbulent air jet, which is used to separate two zones maintained at different temperatures. One of the aims of using an air curtain in the doorway of a building is to minimise the heat losses from the warm room to the cold environment and thus, to save energy. It is important to know how well an air curtain performs in a given operating scenario in order to assess its energy saving potential. In recent literature, it was proposed to use the waterbath experimental technique as a quick and inexpensive tool for testing the performance of an air curtain in a given scenario. The first central objective of the present study is to validate whether results obtained from small-scale waterbath experiments (WB) are adequate to describe the performance of a real-scale air curtain. To this end, we selected scenarios previously investigated by means of WB experiments and conducted real-scale measurements (RS) with a commercially available air curtain device (ACD) in a climate chamber, and RANS numerical simulations (NS) reproducing the configuration of the ACD in the climate chamber. These scenarios include (I) the base case of a downwards discharging air curtain when the doorway is the only connection between the two rooms, (II) the case when there is an additional top-level ventilation pathway between the rooms as well as (III) the case of a downwards blowing heated air curtain when the rooms are again joined only by the doorway. The second main goal of the present study is to verify the previously developed theoretical models for scenarios (II) and (III) by real-scale measurements and numerical simulations. As the main results, we establish that the effectiveness curves for an ACD obtained from WB experiments on the one hand as well as RS and NS measurements on the other exhibit the same general trends but also possess some minor differences for which we offer possible explanations. Furthermore, we find that RS and NS data are very well described by the previously proposed theoretical models in scenarios (II) and (III). The main finding of the present study is that the waterbath technique can be used as a reliable investigation tool to assess the general trends of the performance of an ACD in a given scenario but should be complemented by a small amount of RS or NS measurements if the finer details are important.

Air curtain dust-collecting technology: Investigation of factors affecting dust control performance of air curtains in the developed transshipment system for soybean clearance based on numerical simulation

Transshipment of compacted soybean is characterized by labor-intensive processes, long operating times, and a great amount of dust that cannot be collected by sealed devices. This dust significantly reduces air quality of the workshop and represents a great threat to human health. Solving this problem has been a great challenge in the soybean storage industry. For this reason, in the present study the concept of a transshipment system for soybean clearance was proposed. This system can simultaneously achieve real-time transshipment of falling materials and air curtain control of fugitive dust. The main factors influencing the performance of the air curtain dust control system were investigated using numerical simulation, and the effects of the exhaust-to-pressure ratio K and air curtain outlet velocity V on dust control efficiency were determined. Results showed that the width of the dust-collecting paths increased with increasing K and V values. We also found out that dust-escape paths were mainly concentrated in the transition height between the complete air curtains and local air curtains. At the beginning of the process, dust control efficiency rapidly increased and the increment rate became slower as K increased. When K = 1.5 and V = 5–6 m/s, dust control efficiency reached values up to 95.54–96.27%. Based on numerical simulation results, the prototype transshipment system for soybean clearance was developed, and the effectiveness of air curtain dust control was validated via smoke tracing experiments. After the application of the developed system, occupational lung disease can be significantly reduced, and transshipment efficiency per clearance can be enhanced by approximately 67% (about 50,113￥ can be saved in terms of energy consumption and labor resources). An extra granary can be saved after using the newly developed system for 36.5–52.1 clearances.

Air curtain dust-collecting technology: A simulation study on air jet distribution and departure angle of air curtain generator

The application of long air curtain generators in dust collection for hard-to-seal dust sources is in increasing demand, while the systematical investigation of their performance parameters is very topical. In this study, the FLUENT software package was used to simulate the effects of three structural parameters, namely the air supply groove length, air curtain diameter, and spacing between guide vanes, on the air curtain performance. The first two parameters were found to influence the air supply uniformity directly. Besides, the difference between internal and external pressures was related to the air curtain generator’s critical diameter with specific length: to ensure the required jet power of the air curtain, its actual diameter should exceed this critical value. The spacing adjustment between guide vanes could improve the air curtain skewness by changing the ratio of areas occupied by mechanically and nonmechanically deflected airflows, thereby enhancing the effective air supply length. Finally, the arc-shaped symmetrical guide vanes were shown to outperform folded asymmetrical guide vanes. • Structural parameters of air curtain generator affect the performance of air curtain. • Air curtain generator’s length is limited by the minimum diameter. • Smaller guide vanes spacing improves the effective air supply length. • Arc-shaped guide vanes improve the control of mechanically-deflected airflow.

Study on the Evaluation of Sealing Performance of Horizontal Blowing Air Curtain Installed in Doorways

Air curtains are installed to reduce heat loss due to drafts intruding into the indoor through the open doorways, and play the role of separating two climatic zones and different environmental zones. It is also used to protect the workplace from impurities or to reduce the spread of cigarette smoke in restaurants. Recently, aircraft to provide the individual air barrier by the vertical blowing air curtains have installed a physical barrier in the breathing zone between adjacent seats to protect passengers from COVID-19. The main factors affecting the sealing performance (SP) of the air curtain are the difference of temperature and pressure between indoor and outdoor, and are used to make the proper jet flow an air barrier with the high airtightness. Until now, various types of air curtains are manufactured and sold. Air curtains with the improved SP do not only have a discharge port but also a suction port. This study was conducted to evaluate the SP of the horizontal blowing air curtain according to the discharge pressure, and to select the minimized volume flow rate required for creating the proper zone separation. The volume flow rate of outdoor air intruding into the indoor through the doorways is used to evaluate the SP of the air curtain, and is calculated using the SVE4 proposed by Murakami in this study.

Analysis of phase change material integration in retail display cabinets for energy management

Nowadays, retail stores are highly interested in the application of strategies such as demand response (DR) in refrigerated display cabinets (turning off the cold machine during a certain time) to increase their flexibility in energy management and to facilitate the integration of renewable energy sources. One of the main concerns related to DR deployment is the product and air temperature increase inside the cabinets when the refrigeration machine is turned off. Thermal energy storage TES by phase change materials (PCM) has been demonstrated to be a solution to replace for a limited time the refrigeration unit and maintain the product at low temperature. However, the presence of PCM heat exchanger altered the air curtain performance as well as the thermal behaviour of the display cabinet. Successful integration of PCM needs implementing new cabinet design and operating conditions. Moreover, if this technology is applied for many display cabinets, management strategies need to be considered so that the PCM can be charged and discharged in suitable conditions. If renewable energy sources are available, energy management scenarios combining electrical sources (grid and renewable) and thermal energy storage (PCM) can be planned. The main objectives of the present work are, first, to identify improvement options and optimized parameter ranges that can request the PCM integration in the display cabinet; and second, to test different energy management scenarios at the scale of a supermarket. The study shows that by improving the perforation pattern of the rear duct channel and increasing the fan power, a more homogeneous product temperature distribution and better thermal behaviour of the cabinet are obtained. The effects of the operating conditions (ambient and setpoint temperatures) on thermal behavior, energy consumption and PCM charging/discharging time are analyzed by experimental investigations. A simulation tool was developed to evaluate the global efficiency of a supermarket equipped with PCM display cabinets. For different energy management scenarios, it evaluates the potential of this technology to support DR applications, reduce the electricity contract power of the retail and facilitate the utilization of renewable energy sources, photovoltaic (PV) solar panels in particular. PCM integration allows a reduction of maximal power demand by 8% in the scenario without PV panels and by 13% in the scenario with PV panels.

Full-size experimental assessment of the aerodynamic sealing of air curtains for particulate matter

An air curtain is used to ensure an adequate separation between two compartments that is aimed to restrict, a clean one and a contaminated one. The air curtain performance is improved with the use of an air extraction from the “contaminated” compartment. The aerodynamic sealing of an optimized air curtain is assessed regarding particulate matter. The evaluation using visual assessment of the aerodynamic sealing using a cold smoke source is validated against PM 10 detection. It is shown that the air curtain presents a good aerodynamic sealing for the particulate of PM10 and PM2.5 classes and that the visual assessment method can lead to similar results. An equation was obtained with a view to be used to predict the level of aerodynamic sealing of the air curtain when the exhaust rate becomes too low. Another equation was obtained for predicting the average velocity through the door protected by the air curtain required to obtain an aerodynamic sealing, as a function of the jet parameters (nozzle average velocity and thickness). These test results prove that the air curtain, complemented with an air exhaust from the “contaminated compartment”, is suitable to provide an acceptable aerodynamic sealing for the particulate matter. Practical application: The findings of this research are applicable when it is necessary to retain the contamination due to particulate matter using a soft boundary, as air plane jets. This is applicable to medical care centres to reduce the possibility of contamination due to bacteria between different compartments or in pharmaceutical process units to avoid cross contamination among them.

Air curtain performance: Introducing the adapted separation efficiency

Air curtains (ACs) are plane turbulent impinging jets that are used to separate two environments in terms of heat and mass transfer while still allowing traffic between these environments. The many applications of ACs across a wide variety of industries makes the evaluation of their performance an important but difficult task. The aim of this paper is to introduce a performance indicator, called the adapted separation efficiency, that is suitable for different types of systems that may involve different AC configurations (downward blowing, upward blowing, lateral blowing, multiple jets, etc.) at multiple scales, different transported quantities (heat, water vapor, particles, gases, etc.) subjected to various transport mechanisms (advection, molecular and turbulent diffusion) and varying environmental conditions (gradients in environmental pressure and/or density). It is defined using a conventional efficiency formula. The principle of this performance indicator is illustrated with a generic case study where the performance is evaluated for two basic AC configurations involving cross-jet pressure and density gradients, as well as different jet momentum fluxes. The case study is conducted based on computational fluid dynamics employing validated large eddy simulations.

Effect of Fuel Orientation on the Performance of Air Curtains in Confining Fire and Smoke Propagation in Informal Shopping Malls

Effect of Fuel Orientation on the Performance of Air Curtains in Confining Fire and Smoke Propagation in Informal Shopping Malls

Wind pressure coefficients for buildings with air curtains

An air curtain is often installed at a building entrance as an air barrier to reduce infiltration and resultant energy and air quality concerns. Due to its direct contact with the ambient environment, wind could affect the air curtain’s performance significantly, whereas its interaction with the wind has not been well understood. This study carried out a series of experiments on a sub-scaled building model with an air curtain in an atmospheric boundary layer wind tunnel. A CFD model was also built to further investigate the air curtain jet interactions with the wind. The CFD model was verified and validated through Particle Image Velocimetry measurements for different air curtain and wind conditions and in terms of the function of the dimensionless air infiltration rate versus the dimensionless pressure difference across the air curtain. This study defined the wind pressure coefficient for air curtains based on their performance under wind compared to that without wind. The wind pressure coefficient was found to be constant for different air curtain supply speed, supply angle, and wind speed, but varies with wind direction, so its profile was provided as a function of wind direction. This study provides insights into air curtain performance under various wind conditions.

Impact of Flow Blowing and Suction strategies on the establishment of an aerodynamic barrier for solar cavity receivers

This study compares two aerodynamic approaches to minimize convective losses from cavity receivers, namely blowing and suction. A laboratory-scale cavity receiver was operated in a large wind tunnel at varying wind speed and tilt angle. The inner surface of the cavity was heated to a constant temperature of 300 °C by finely controlled electrical heaters. The measured electric energy required to maintain the heaters at the same temperature was used to provide a direct measure of losses from the receiver. An air curtain was engineered to provide curtain of air blown either downward or upwards across the aperture. Suction was alternatively applied through a nozzle positioned below the aperture for a series of suction flowrates. A numerical study was also conducted using a commercial CFD package and validated with available data. It was found that the upward blowing air curtain performs better than the downward curtain for the buoyancy dominant conditions. Moreover, the measured effectiveness of the downward blowing air curtain at tilt angle of the cavity of 45° showed that the application of air curtain with higher velocities increases the convective heat losses over the case with no air curtain. When comparing the performance of air curtain with air suction, it was found that for the low range of relative momentum ratio of curtain to wind flow, suction performs better than blown air. Finally, this study highlights the need for adaptable strategies, based on operating condition, to minimize heat losses and improve the thermal efficiency of cavity receivers.

A novel circulated air curtain system to confine the transmission of exhaled contaminants: A numerical and experimental investigation.

Air curtain is an efficient device for cutting off airflow and confining contaminants. Inspired by the ability, a circulated air curtain composed of end-to-end plane jets generated by a relay of air pillars is proposed to confine exhaled contaminants in this study. Furthermore, the optimization study of computational fluid dynamics (CFD) is conducted to explore cutting-off performance and find better design parameters under different conditions, i.e., human-curtain distance, enclosure shape, jet velocity from air pillar, and exhalation modes. The multidirectional blockage and vortex-like rotative transmission routes of exhaled airflow are observed when air curtain exists. Results indicate that contaminants are concentrated around the source. The average mole fraction of exhaled contaminants outside air curtain under different human-curtain distance decreases 4.3%–19.6% compared to mixing ventilation with same flux. Shortening the human-curtain distance can improve the performance of air curtain and may change the direction of exhaled airflow. Moreover, It has better performance when the enclosure shape is close to a circle. Higher jet velocity is better for improving the confinement performance, but the trend is not very obvious as velocity increases. For exhalation modes, it is more challenging to control exhaled contaminants for intense exhalation activity (such as coughing) in steady simulation, but results in transient simulation show better performance when coughing only once. These results can provide a reference for the subsequent design and improvement in applying air curtain in hospital wards or other places, especially during the period of flu outbreak.Electronic Supplementary Material (ESM)Supplementary material is available in the online version of this article at 10.1007/s12273-020-0667-5. The ESM file presents the animation of the droplet trajectory from the droplet birth at 0 s to 8 s

Using air curtains to reduce short-range infection risk in consulting ward: A numerical investigation.

Air curtains is promising in reducing the short-range infection risk in hospitals. To quantitatively evaluate its performance, this paper explores air curtains equipped on normal consulting desk to avoid doctor’s direct exposure to the patient exhaled pollutants. A numerical investigation is conducted to evaluate the effects of supply air velocity and angle on cutting off performance. Simulation results show that the average mass fraction of exhaled pollutants decreases significantly (70%–90%) in the consulting ward, indicating satisfying performance of air curtains. Increasing supply air velocity is demonstrated to be conducive in forming full air curtains, whereas an excessively high supply air velocity may be of adverse effects by entraining exhaled flow. Besides, the supply air angle is also critical due to its coupling with supply air velocity. It is found that larger angle (0°–40°) is better where velocity is less than 3 m/s, otherwise a small angle (20°) is preferable where velocity is larger than 3 m/s. Exhaled flow could be well suppressed at the supply air angle 20° but moves over air curtains at 40°. This study can provide effective and intuitive guidance in applying air curtains in consulting wards.Electronic Supplementary Material (ESM) Supplementary material is available in the online version of this article at 10.1007/s12273-020-0649-7. The ESM files include the animation of patient exhaled droplets from the droplet birth at 0 s to 5 s under the supply air angle 0°, 20°, 40°, at supply air velocity 3 m/s.

Air curtain effectiveness rating based on aerodynamics

An air curtain installed at a building entrance acts as a barrier against infiltration/exfiltration of airflow between the outdoor environment and the indoor space. Several factors may affect air curtain performance, including air discharge velocity, angle, door height and width, and indoor and outdoor conditions. The current methodological standards/codes evaluate air curtain performance based on 1). aerodynamics performance characterization through the measurements of the jet velocity distribution and degradation, and 2). the laboratory measurements of their effectiveness in terms of blocking infiltration/exfiltration rates with/without air curtains under different operating conditions, i.e. pressure difference across doors. The 1st method is easier to conduct but cannot directly evaluate the effectiveness of an air curtain in reducing infiltration/exfiltration. The 2nd method can evaluate each specific unit, though the tests are often prohibitively costly and time-consuming. This study developed a new cost-effective method to assess the aerodynamic performance of an air curtain with respect to its capability of reducing infiltration/exfiltration. This method was demonstrated by a case study and validated against previous experimental data. The new method was found to be more efficient and cost-effective for various air curtain products and installation scenarios, as compared to existing methods.

The Effect of Round Flow Path Discharger and Back Panel Open Ratio on a Performance of Open Refrigerating Showcase

Numerical study is conducted to confirm the effect of round flow path control and back panel open ratio on a performance of open refrigerating showcase in this study. The rounding control is applied to flow path of air discharger in various radii and the punched panel with various open ratios is applied to back panel of showcase. These structural changes have a significant impact on its aircurtain performance because both changes can affect flow pattern of showcase. To prove it, the two-dimensional steady simulation is performed using [Formula: see text]–[Formula: see text] turbulent model. The performance of showcase is assessed using entrainment factor which is a ratio between cooled air and ambient air at the suction of refrigerating part. As a result of simulation, the curved path at air discharger reduces the entrainment factor by a maximum 9% less than typical design. The curved flow path removes the dead zone at the honeycomb structure of discharger. In addition, it is found that there is an optimal back panel open ratio at the storage space of the showcase. When the back panel open ratio is 0%, the cooled air from the discharge is attached to the cold storage area because of the Cowanda effect. However, the Cowanda effect is eliminated when back panel open ratio increases. Results address that the entrainment factor remains almost the same at back panel open ratio 3.93% or more. Lastly, the simulation of showcase with product in cold storage area is conducted to confirm the structure changes effect on performance of real use showcase according to KS Standard.